******WARNING: LONG POST; SPOILERS SPOILERS SPOILERS AHOY!******* =D
Hmm, the only person I've seen who calls Vimes "Sam" (other than Ridcully) is Sybil. Everyone else calls him one of these names:
- "Sir" (Carrot, Angua, Nobby, Willikins the Butler)
- "Commander" (most of the rest of the...